With PVC, when the poly vinyl chloride gets hot, it releases nasty molecules that can react during combustion and make nasty deposits on your cylinder walls. Engines create a ton of heat, and that heat causes the PVC to heat up, ionizing some of the poly vinyl chloride and chemicals used to cure it and releasing them into the intake air. I'm sure it won't do anything in a year - it might not even do anything in two years - but over time, the build up of gunk on cylinder walls can cause problems. Honda forums have shown this. But maybe it'* just the ricer engines.